Former HP CEO Mark Hurd has joined Oracle as co-president and board member, effectively taking the place of former Oracle President Charles Phillips who resigned Monday.

The announcement came from Oracle Chairman and CEO Larry Ellison on Monday's Labor Day holiday but drew wide attention with the return of the business week. Oracle shares rose 6 percent in trading Tuesday on news of Hurd's arrival.

But by mid-afternoon Tuesday, HP had filed a civil complaint against Hurd in California Superior Court, alleging that the former CEO had signed agreements to protect HP trade secrets and confidential information.

"HP intends to enforce those agreements," reads a post in HP's corporate blog, and also offers a link to download the PDF of the complaint.

The complaint reads in part: ”In his new positions, Hurd will be in a situation in which he cannot perform his duties for Oracle without necessarily using and disclosing HP's trade secrets and confidential information to others."

Both Hurd and Phillips were involved in scandals involving personal relationships, and while HP and Oracle have played down the episodes, analysts don't consider Hurd's arrival to be public image marketing.

Andrew Bartels, vice president and principal analyst at Forrester Research, says while Ellison and Hurd are known to be friends, the justification to bring Hurd on is understandable. "Hurd is a hardware guy and Oracle has Sun, so there's good motivation to bring him to do what he can to grow Oracle's hardware business."

Besides his time at Oracle, Hurd was CEO at NCR, which owned and later spun off data warehousing database and hardware provider Teradata.

Oracle's announcement also said that co President Safra Katz will remain in her current role with Oracle.